The invention relates to a method for producing a metal hose coupling which is adapted to be mounted permanently on the end of a pressure hose for pressurized hydraulic oil, which hose coupling then can create a fluid connection between the hose and an attachment member, the hose coupling having at least one hose nipple which, in the fitted state, projects into the hose and a connecting part, which is designed to form a connection to the attachment member, the hose coupling furthermore comprising, for each hose nipple, a deformable sleeve which, in the fitted state, rests around that part of the hose which has been pushed onto the hose nipple and, with deformation to the sleeve, holds the hose on the hose nipple, an oil passage extending through the connecting part and the at least one hose nipple.
The present invention also relates to a hose coupling which is produced using the method according to the invention.
Metal hose couplings are generally known for the purpose of coupling hydraulic pressure hoses, which are usually provided with a reinforcement, to an attachment member, such as a hydraulic pump, a valve, a cylinder, etc.
NL 1001273 and DE 28 49 133 show 90xc2x0 elbow hose couplings with a single hose nipple which is at right angles to the connecting part, which is designed as an insertion part.
Hitherto, two components, namely the hose nipple and the connecting part, have been used as a basis for the production of hose couplings of this nature. In this case, the connecting part is provided with a hole for accommodating the hose nipple. These two components are joined together by hard soldering in order, on the one hand, to create a strong bond between the two components and, on the other hand, to create a seal between the two components which is able to withstand the high pressure of the hydraulic oil.
Hard soldering has the drawback that it is impossible to see from the outside whether the connection between the hose nipple and the connecting part is liquid-tight. For this reason, each hose coupling has to be tested separately for leaks, and even then there is still the problem that the ability to withstand a brief pressure test does not definitively mean that the soldered seam will remain sealed for a prolonged period. Subsequent leakage may occur in particular under the influence of vibrations.
A further drawback is that solder may enter the passage in the hose coupling. If this passage has a small cross section, for example of 1 to 2 millimeters, this may lead to the passage becoming blocked. Furthermore, solder which has entered the passage may become detached over the course of time and may then have an adverse effect on, for example, the action of valves in the hydraulic system.
Moreover, hard soldering is an expensive process, since the soldering of hose couplings of this nature has to take place in a furnace in which there is a vacuum or an inert gas present.
The object of the present invention is to propose measures which provide an improved hose coupling and, at the same time, enable the cost price to be reduced.
The present invention provides a method for producing a hose coupling having a connecting part and at least one hose nipple, which hose coupling is produced as a single-piece body by means of the metal injection moulding process.
The present invention is based on the insight that the metal injection moulding process, which is known per se, can be used to produce a single-piece body with the tolerances required for hose couplings. Since this process comprises the injection moulding of a preform, there is a risk of burrs being formed on the product obtained. Burrs in hose couplings are particularly undesirable on the surface of the hose nipple, since the hose would then press on such a burr with a great pressure, and would then be cut into, leading to leakage.
It has been found that the method according to the invention is able to provide a hose coupling without subsequent machining being required in order to remove any burrs.
As is known, injection moulding results in the formation of burrs as a result of the mould parts not completely adjoining one another. Consequently, a preferred embodiment of the invention provides for the contact surfaces of the injection mould parts along the edges which form the mould cavity for the hose nipple to be locally raised, for example by {fraction (1/100)}th millimeter. As a result, the mould-closing force is concentrated at these edges and the formation of burrs on the hose nipple is avoided.
In combination with the use of an injection mould of this nature, or as a separate measure, it is then possible for the preform obtained by injection moulding to be brushed with a soft brush prior to sintering. In this way, projecting burrs are easily removed without damage to the preform.
It has therefore proven possible for the metal injection moulding process to be carried out in such a way that no further machining is required in order to remove burrs. It will be clear that, by making use of the metal injection moulding process, which is known per se, all the drawbacks of the known production method referred to in the introduction are eliminated.
The method according to the invention is particularly advantageous for the production of xe2x80x9cangledxe2x80x9d hose couplings, in which the at least one hose nipple does not lie in line with the connecting part, but obviously it is also advantageous for the production of straight hose couplings.
In a preferred embodiment, the invention provides for the single-piece body of the hose coupling to be made from stainless steel, preferably RVS 316, so that there is no longer any need for a separate treatment in order to achieve the desired resistance to corrosion.
The present invention also relates to a hose nipple produced using the metal injection moulding process.
The present invention will be explained below with reference to the drawings.